Increasing use of portable computing or electronic devices has led to increased reliance on battery power. Devices such as cell phones, personal digital assistants (PDAs), small computers, e-mail devices, audio players, video players, etc., are complex devices often having many functions and subsystems. Typically, one battery is used to provide all of the device's power needs.
Some devices, such as portable computers, allow power-management. Thus, it is possible to designate when a portable computer will go into a low-power mode after an interval of non-use. Low power modes can include standby, hibernate, and the like. Other ways to manage power can include controlling subsystems such as the display screen, disk drive, etc., and placing these subsystems in higher or lower power modes according to determinations made by hardware or software running in the device, or according to determinations made by a user of the device. However, because battery power is so important to a portable device, it is desirable to provide more control and flexibility over the device's use of battery power and in how a device interacts with a battery.